Developing agent, method for manufacturing the same, image forming apparatus

ABSTRACT

0.01 to 5% by weight of the metal soap is added to the yellow toner and black toner.

BACKGROUND OF THE INVENTION

The present invention relates to an image forming apparatus used for,for example, an electrostatic type recording apparatus orelectrophotographic device, an image forming method and a developingagent applied to these apparatus and method.

Conventionally, there is a technique, as disclosed in, for example, Jpn.Pat. Appln. No. 2001-51443, designed to reduce abrasion of thephotosensitive layer of a photoreceptor drum by externally adding ormixing metal soap to a developing agent. In this technique, the metalsoap is supplied together with the developing agent to the surface ofthe photoreceptor, and therefore it is considered that the abrasion ofthe photoreceptor by the cleaning blade can be reduced due to theslipping effect of the metal soap. As the lifetime of the photoreceptordrum is prolonged, it becomes possible to provide print images at a lowcost. However, with the addition of a metal soap, the fluidity of thedeveloping agent is lowered. As a result, a deterioration of image,which is called rough surface, occurs. In particular, full-color imagesof the skin colors of persons, blue sky or the like are significantlydeteriorated. In order to avoid this, it is conventionally necessary tolimit the amount of addition of the metal soap.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to reduce the abrasion of thephotosensitive layer and provide a high image-quality full-color imageat a low cost.

According to the first aspect of the present invention, there isprovided an image forming apparatus comprising:

an image carrier;

a plurality of developing devices located to face the image carrier andconfigured to form a developing agent image by developing a staticlatent image formed on the image carrier;

a transfer device configured to transfer the developing agent image ontoa transfer material;

a cleaning device provided in a downstream of the transfer device andconfigured to collect a remaining developing agent on the image carrier;and

a fixing device having a heating member and configured to fix thedeveloping agent image transferred on the transfer member,

wherein one of the plurality of developing devices contains ayellow-color developing agent containing a yellow coloring agent, abinder resin and 0.01 to 5% by weight of a metal soap and another one ofthe plurality of developing devices contains a black-color developingagent containing a black coloring agent, a binder resin and 0.01 to 5%by weight of a metal soap.

Further, according to the second aspect of the present invention, thereis provided an image forming method comprising:

forming a static latent image on an image carrier;

forming a developing agent image by using a developing agent selectivelysupplied from a plurality of developing devices including a yellow-colordeveloping device containing a yellow-color developing agent containinga yellow coloring agent, a binder resin and 0.01 to 5% by weight of ametal soap and a black-color developing device containing a black-colordeveloping agent containing a black coloring agent, a binder resin and0.01 to 5% by weight of a metal soap;

transferring the developing agent image onto a transfer material;

cleaning a developing agent remaining on the image carrier after thetransferring with use of a cleaning unit; and

fixing the transferred developing agent image onto the transfer member.

Furthermore, according to the third aspect of the present invention,there is provided a combination of developing agents applied to an imageforming method apparatus including a plurality of developing devicesconfigured to form a developing agent image by developing a staticlatent image, comprising: a yellow-color developing agent to becontained in one of the plurality of developing devices, containing ayellow coloring agent, a binder resin and 0.01 to 5% by weight of ametal soap and a black-color developing agent to be contained in anotherone of the plurality of developing devices, containing a black coloringagent, a binder resin and 0.01 to 5% by weight of a metal soap.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be leaned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a schematic diagram showing the structure of an example of theimage forming apparatus according to the present invention;

FIG. 2 is a schematic diagram showing the structure of another exampleof the image forming apparatus according to the present invention; and

FIG. 3 is a schematic diagram showing a different version from thatshown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

An image forming apparatus according to the first aspect of the presentinvention, comprises:

an image carrier;

a plurality of developing devices located to face the image carrierincluding a yellow-color developing device which contains a yellow-colordeveloping agent containing a yellow coloring agent, a binder resin and0.01 to 5% by weight of a metal soap and a black-color developing devicewhich contains a black-color developing agent containing a blackcoloring agent, a binder resin and 0.01 to 5% by weight of a metal soap;

a transfer device configured to transfer the developing agent image ontoa transfer material;

a cleaning device provided in a stage behind the transfer unit andconfigured to collect a remaining developing agent on the image carrier;and

a fixing device having a heating member and configured to fix thedeveloping agent image transferred on the transfer member.

Further, the image forming method according to the second aspect of thepresent invention, comprises:

forming a static latent image on an image carrier;

forming a developing agent image by using a developing agent selectivelysupplied from a plurality of developing devices provided for a pluralityof colors of developing agents, respectively;

transferring the developing agent image onto a transfer material;

cleaning a developing agent remaining on the image carrier after thetransferring with use of a cleaning device; and

fixing the transferred developing agent image onto the transfer member.

Furthermore, the developing agent according to the third aspect of thepresent invention is applied to the above-described image formingapparatus, comprises: a yellow-color developing agent to be contained inone of a plurality of developing devices, containing a yellow coloringagent, a binder resin and 0.01 to 5% by weight of a metal soap and ablack-color developing agent to be contained in another one of aplurality of developing devices, containing a black coloring agent, abinder resin and 0.01 to 5% by weight of a metal soap.

The black developing agent and yellow developing agent are veryfrequently used in full-color image formation. Further, with the blackdeveloping agent and yellow developing agent, the roughness of imagequality and the like are not prominent even if a metal soap is added.Thus, even in the case where a metal soap is added to the blackdeveloping agent and yellow developing agent only, the roughness of theimage quality and the like do not become prominent, and the metal soapcan be fully distributed over an image carrier. Further, the black andyellow developing agents collected by the respective cleaning devicesare reserved therein, and the metal soap can be further supplied to theimage carrier.

With use of the present invention, the metal soap can be fully suppliedonto the image carrier. Therefore, it is possible prevent a flaw beingmade on the image carrier, as it is scratched with, for example, thecleaning blade provided in the cleaning device and a carrier interposedbetween transfer rollers or the like, provided in the transfer device.Further, since the metal soap is not used excessively, the deteriorationof the image quality, which may be caused by the metal soap, can besuppressed, thereby making it possible to obtain an excellent image.

As described above, according to the present invention, a particularcombination of developing agents with a metal soap blended thereto, isapplied to an image forming device which employs a developing devicehaving a plurality of developing devices. Thus, the abrasion of thephotosensitive layer is suppressed, and a high-quality full-color imagecan be formed at a low cost.

These developing devices can further include a magenta developing devicein which a magenta-color developing agent is contained and a cyandeveloping device in which a cyan-color developing agent is contained.With these developing devices, images can be formed in full-color.

The metal soap can be added not only to the black developing agent andyellow developing agent, but also to the magenta developing agent andcyan developing agent. Preferably, a developing device containing amagenta developing agent containing a magenta coloring agent, binderresin, and a metal soap in an amount less than the amount of the metalsoap contained in the yellow coloring agent; and a developing devicecontaining a cyan developing agent, binder resin, and a metal soap in anamount less than the amount of the metal soap contained in the cyancoloring agent can be included in the image forming device according tothe present invention.

The total of the contents of the metal soaps should preferably be 0.02to 20% by weight. If the total amount is less than 0.02% by weight,there is such a tendency that the abrasion effect of the photoreceptorcannot be obtained, whereas if the total amount exceeds 20% by weight,there is such a tendency that an excessive slipping effect results dueto the amount of the metal soap, thus creating a drawback of cleaningerror or the like.

Examples of the metal soap are zinc stearate, aluminum stearate, calciumstearate, magnesium stearate, zinc behenate, aluminum behenate, calciumbehenate, magnesium behenate, zinc laurate, aluminum laurate, calciumlaurate and magnesium laurate.

Examples of the binder resin which can be used for the developing agentare polyester resin, polystyrene resin, styrene-acrylate copolymerresin, polyester-styreneacrylate hybrid resin, epoxy resin,polyether-polyol resin.

Examples of the wax which can be used for the developing agent arenatural waxes such as rise wax and carnauba wax, a petroleum wax such asparaffin wax, and synthesized waxes such as fatty acid ester, fatty acidamide, low molecular weight polyethylene and low molecular weightpolypropylene.

Examples of the coloring agent are carbon black, organic and inorganicpigments and dyes. Although it is not particularly limited, examples ofthe carbon black are acetylene black, furnace black, thermal black,channel black and ketchen black.

Examples of the pigment and dye are Pigment Yellow 180, Fast Yellow G,Benzidine Yellow, Indofast Orange, Irgazine Red, Carmine FB, Carmine 6B,Permanent Bordeaux FRR, Pigment Orange R, Pigment Red 122, Lithol Red2G, Lake Red C, Rhodamine FB, Rhodamine B Lake, Phthalocyanine Blue,Pigment Blue 15-3, Brilliant Green B, Phthalocyanine Green, andQuinacridon may be used singly or in combination.

If necessary, other additives such as a charge controller, aninterior/exterior lubricant, a cleaning additive, and a fluidizationagent may be used.

In the meantime, these developing devices of the present invention canbe arranged in the following manners. For example, four developingdevices can be individually arranged around the image carrier. In thiscase, each of the devices is set to face the image carrier. It is alsopossible that the four developing devices are arranged in four sectionsformed within one rotation-type developing unit. Further, it is furtherpossible that three of the four developing devices are arranged in threesections formed within one rotation-type developing unit, and the otherone single color (monochrome) developing device is provided to beindependent from this rotation-type developing unit.

Next, the present invention will now be described in more detail withreference to drawings.

FIG. 1 is a schematic diagram showing the structure of an example of theimage forming apparatus according to the present invention.

The image forming apparatus includes an image forming portion 1. Theimage forming portion 1 includes a photoreceptor belt 2 serving as animage carrier. The photoreceptor belt 2 is stretched over between aplural number of first to fifth rollers 3 a to 3 e such as to be able torun along the direction indicated by an arrow at a predeterminedtension.

Around the photoreceptor belt 2, a charger device 4 for charging thephotoreceptor belt 2 at a predetermined potential along its runningdirection, an exposure device 4 serving as an image forming device forforming an electrostatic latent image on the charged photoreceptor belt2 and first to fourth developing devices 6 a to 6 d for supplying tonerserving as a developing agent onto the latent image formed on thephotoreceptor belt 2. Further, around the photoreceptor belt 2, arotatable intermediate transfer member 7 for temporarily holding a tonerimage formed on the photoreceptor belt 2 and a cleaner device 9 forremoving the toner remaining on the photoreceptor belt 2 are arranged inthe belt's running direction. On an upper side of the intermediatetransfer member 7, a cleaner 8 for cleaning the intermediate transfer 7is provided.

The photoreceptor belt 2 is arranged in such a manner that the portionstretched over between the first and second rollers 3 a and 3 b isplaced in tight contact with the circumferential surface of theintermediate transfer member 7, and the portion stretched over betweenthe third and fourth rollers 3 c and 3 d faces via certain gaps thedeveloping units 6 a to 6 d.

It should be noted that either one of the first to fifth rollers 3 a to3 e is connected to a drive motor (not shown), and due to the rotationof the drive motor, the first to fifth rollers 3 a to 3 e are rotated ata predetermined speed in the direction indicated by the arrow.

On the other hand, underneath the image forming portion 1, a sheetcassette 12 for loading sheets P serving as a transfer material having apredetermined size is provided. A paper feeding roller 13 is provided inthe sheet cassette 12 in order to feed out the sheets P one by one.

Between the sheet cassette 12 and the intermediate transfer member 7, aconveying path 14 for conveying a sheet P towards the intermediatetransfer member 7, is provided along the vertical direction. A transferroller 16 serving as a transfer device is provided in the conveying path14 such that the roller faces the intermediate transfer member 7, andthe transfer roller serves to transfer the toner image formed on theintermediate transfer member 7 onto the sheet P.

An aligning roller 18 is provided on an upstream side to the transferroller 16 with regard to the sheet conveying direction. The aligningroller 18 temporarily stops a sheet P conveyed by the conveying system14, and then corrects the inclination of the sheet P with respect to theconveying direction, and sets the leading end of the sheet P to matchwith the leading end of the toner image on the intermediate transfermember 7.

On a downstream side to the transfer roller 11 with regard to the sheetconveying direction, a separating device 19 for separating the sheet Pon which the toner image has been transferred, from the intermediatetransfer member 7 by applying an AC charge thereto, and a fixing device20 for fixing the toner image transferred on the sheet P, to the sheet Pare arranged.

Next, the full-color printing operation of the image forming apparatusdescribed above will now be described.

First, the surface of the rotating photoreceptor belt 2 is chargeduniformly at a predetermined potential by the charging device 4.Subsequently, an exposure corresponding to a yellow image is carried outon the photoreceptor belt 2 by the exposing device 4, so as to form astatic latent image. The latent image is developed as yellow toner issupplied thereto from a yellow developing device 1 a, and thus obtaineddeveloping agent image is transferred onto the intermediate transfermember 7. After the transferring operation, the photoreceptor belt 2 isseparated from the intermediate transfer member 7, and then it isphoto-destaticized by a charge-removing device which is not shown in thefigure.

On the other hand, the toner remaining on the photoreceptor belt 2without having been transferred to the intermediate transfer member 7 iscleaned with the cleaner device 9. The toner removed by the cleaning iscollected in a waste toner box which is not shown in the figure. After awhile, the photoreceptor belt 2 is re-charged by the charging device 4and thus an exposure corresponding to a magenta image is carried out bythe exposure device 5, thereby forming a static latent image thereon.This static latent image is developed with a magenta toner by a magentadeveloping unit 6 b, and thus this magenta toner image is transferredonto the intermediate transfer member 7 to be interposed on the yellowimage on the transfer member. A similar procedure to the above iscarried out for a cyan image and a black image as well, thereby forminga four-color multiple layered toner image on the intermediate transfermember 7.

After the image formation described above, a sheet P is fed between theintermediate transfer member 7 and the transfer roller 16, and thefour-color multiple layered toner image is secondarily transferred inbatch on the sheet P. The sheet P on which the four-color multiplelayered toner image has been transferred, is separated from theintermediate transfer member 7 by a separator charger 19. This separatedsheet P is conveyed to the fixing device 20, where the toners are fixedto obtain a color image.

On the other hand, the toner portion remaining unused after transferringthe image on the sheet P, remains on the intermediate transfer member 7.The remaining toner is cleaned by a cleaner 8 which is brought intocontact with the intermediate transfer member 7 after finishing thesecondary transfer operation.

It should be noted that while the above-described four-color multiplelayered image is being formed on the intermediate transfer member 7, thecleaner 7 is separated from the intermediate transfer 7.

In the meantime, FIG. 2 is a schematic diagram showing the structure ofanother example of the image forming apparatus according to the presentinvention.

As shown in the figure, a photoreceptor drum 101 serving as an imagecarrier is a cylindrical laminate-type organic photoreceptor, and isprovided rotatable in the direction indicated by the arrow as shown inthe figure.

Around the photoreceptor drum 101, the following members are arrangedalong its rotating direction.

First, a developing device 109 which contains a developing agent andserves to develop, with this developing agent, a static latent imageformed by an exposing unit 107 develop is provided such as to face thephotoreceptor drum 101. On a downstream of the developing device 109, anintermediate transfer belt 120 supported to be able to run in thedirection indicated by the arrow in the figure by three rollers isprovided such as to face the photoreceptor drum 101. As the material ofthe intermediate transfer belt, those having sufficient properties interms of charge retaining power and uniform surface state are requiredbecause the belt must temporarily hold the developing agent.

Further, a transfer roller 130 is set on the intermediate transfer belt120 and a paper-feeding cassette (not shown) which stores sheets isprovided near the transfer roller 130. Paper sheets are conveyed in thedirection indicated by an arrow 107 from the paper-feeding cassette andthen sent between the intermediate transfer member 120 and transfermeans 130.

On a downstream side to the photoreceptor drum 101, a blade cleaningdevice 117 and a charge-removing lamp 119 are provided. The bladecleaning device 117 is designed to remove the remaining portion of thedeveloping agent by scraping it off with a blade which is not shown inthe figure, after the transfer of a developing agent image. Thecharge-removing lamp 119 is a tungsten lamp which canphoto-destaticizing the surface of the photoreceptor drum 101 after thetransfer of an image. When the destaticization with the charge-removinglamp 119 is finished, one cycle of an image formation is completed. Forthe next image formation, if there is, the photoreceptor drum 101,currently uncharged, is re-charged.

Then, the sheet on which the developing agent image has been transferredby the transfer roller 130 is sent to the fixing device 140.

The developing unit 109 is sectionalized into four sections as shown inthe figure, and these sections respectively include a yellow developingportion 109 a, a magenta developing portion 109 b, a cyan developingportion 109 c and a black developing portion 109 d. The developing unit109 is arranged rotatable such that the yellow developing portion 109 a,the magenta developing portion 109 b, the cyan developing portion 109 cand the black developing portion 109 d can face the photoreceptor drum101 in this order one after another. These developing portions contain,respectively, a yellow developing agent, a magenta developing agent, acyan developing agent and a black developing agent.

The image forming operation by an image forming apparatus having such astructure as above will now be described.

First, with use of charging means which is not shown in the figure, abias voltage is applied onto the photoreceptor drum 101 so as touniformly charge the surface of the photoreceptor drum 101. Next, alight exposure 107 is applied onto the surface of the photoreceptor drum101, and thus a first static latent image is formed thereon. Then, thedeveloping portion 109 a is disposed to face the first latent image andsupplies the yellow developing agent thereto, thereby forming a yellowdeveloping agent image.

To the intermediate transfer belt 120, a bias voltage is applied frompower feeding means 137. As the bias voltage is applied, a transferelectric field is formed between the photoreceptor drum 101 and theintermediate transfer belt 120. First, the yellow developing agent imageformed on the photoreceptor drum 1 is transferred to the intermediatetransfer belt 120.

After that, the remaining portion of the yellow developing agent and theremaining charge on the photoreceptor drum 101 are removed by thecleaning device 117 and the charge-removing means 119, respectively.

On the photoreceptor drum 101 from which the yellow developing agent andcharge have been removed, a second static latent image is formed with alight exposure 107. The developing device is rotated by ¼, and thedeveloping unit 109 b is disposed to face the photoreceptor drum 101.

In this manner, the magenta developing agent is supplied to the secondstatic latent image, thereby forming a magenta developing agent image.After that, to the intermediate transfer belt 120, a bias voltage isapplied once again from the power feeding means 137. As the bias voltageis applied, a transfer electric field is formed between thephotoreceptor drum 101 and the intermediate transfer belt 120. Thus, themagenta developing agent image formed on the photoreceptor drum 1 istransferred further to the intermediate transfer belt 120 on which theyellow developing agent image has been transferred.

With regard to the cyan developing agent and black developing agent,similar steps are repeated and thus yellow, magenta, cyan and blackdeveloping agent images are formed as a multiple layers.

To a transfer position situated between the intermediate transfer belt120 on which the image formed by multiple transfer is carried, and thetransfer roller 130, a paper sheet P is conveyed. Then, the yellow,magenta, cyan and black developing agent images formed on theintermediate transfer member 120 are transferred to the paper sheet P.

The paper sheet P which carries the image formed by the multipletransfer is conveyed in the direction indicated by the arrow 107, andsent to the fixing device 140 which includes a heating roller 135 and apressure roller 136. As the paper sheet P is allowed to pass through theheating roller 135 and the pressure roller 136 while the image formed onthe sheet being in contact with the heating roller 135, the image isfixed onto the sheet P. Thus obtained image has a good quality.

In the image forming apparatus described above, a particular combinationof developing agents defined by the present invention is used. Anexample of the developing agent is that made of a yellow colordeveloping agent containing a yellow coloring agent, a binder resin anda metal soap at 0.01 to 5% by weight, a magenta color developing agentcontaining a magenta coloring agent and a binder resin, a cyan colordeveloping agent containing a cyan coloring agent and a binder resin,and a black color developing agent containing a black coloring agent tobe contained in one of a plurality of developing units, and a metal soap0.01 to 5% by weight.

FIG. 3 is a schematic diagram showing another version of the apparatusshown in FIG. 2.

As shown in the figure, this image forming apparatus has a similarstructure to that shown in FIG. 2 except for the followings. That is, inplace of the developing device 109, a developing unit comprising arotation-type developing device 209 including a yellow developingportion 209 a, a magenta developing portion 209 b and a cyan developingportion 209 c, and another developing device 409 consisting of afixation-type black developing portion 309 is used in this apparatus.

The image formation by this apparatus is carried out in a similar mannerto that of the apparatus shown in FIG. 2 except for the followings. Thatis, after the first static latent image is developed, the developingunit is rotated by ⅓ until the second static latent image is developed,and the black developing agent is supplied to the fixation-type singlecolor developing portion.

The present invention will now be described in more detail by presentingspecific examples.

First, in order to examine the amount of the metal soap, the abrasion ofthe photoreceptor, the properties such as the roughness of image, thefollowing tests were carried out.

Test 1

First, the following toner material of the specified color was prepared.

Magenta-color toner composition

Magenta color agent: PIGMENT RED 184 . . . 4 parts by weight

CCA: Zr metal complex (manufactured by Hodogaya Kagaku K.K.) . . . 1part by weight

Binder Resin: Polyester resin . . . 95 parts by weight

The toner particle material given above was uniformly mixedpreliminarily with a Henschel mixer (manufactured by Mitsui Kouzan K.K),followed by melting and kneading the resultant mixture by using apressurizing kneader. The kneaded material thus obtained was dried andthen roughly pulverized in a pin mill. Further, the roughly pulverizedmaterial was finely pulverized by a I-type jet mill machine(Manufactured by Hosokawa Micron K.K.), followed by classifying thefinely pulverized material into a size of 8 μm so as to obtain tonerparticles.

Further, 1 part by weight of silica treated with a silane coupling agentand 0.01 part by weight of zinc stearate were added to 100 parts byweight of thus obtained toner particles, and mixed in a Henschel mixerso as to obtain a toner.

6% by weight of the toner thus prepared was mixed with 94% by weight ofa ferrite carrier coated with a silicone resin so as to obtain a magentadeveloping agent.

Thus magenta developing agent thus obtained was applied in a developingdevice of “Premarju 455” (manufactured by Toshiba Corporation) so as toform images consecutively for 30,000 sheets.

In the meantime, the following tests were carried out in the respectivesteps described above.

Print Wear-out-proof Test

The diameter of the photoreceptor was measured in advance, and imageswere formed continuously on 30,000 sheets. Then, the diameter of thephotoreceptor was measured once again. In order to examine the state ofthe abrasion of the photoreceptor, the amount of change in the diameterof the photoreceptor between before and after the image formation wascalculated. The obtained results were presented in TABLE 1 below.

Cleaning Error Test

After images were formed continuously on 30,000 paper sheets, set-solidimages of size A3 were continuously collected. Then, the surface of thephotoreceptor and the surface of the image were observed by eye, so asto confirm whether or not there is a cleaning error.

The evaluation was made on the basis of the following criteria. That is,{circumflex over (∘)} indicates the case where there is no error eitheron the surface of the photoreceptor or on the surface of the image after100 sheets of continuous image formation, ◯ indicates the case wherethere is no error on the surface of the photoreceptor but on the surfaceof the image after 100 sheets of continuous image formation, Δ indicatesthe case where there is no error on the surface of the photoreceptor buton the surface of the image after 10 sheets of continuous imageformation, and X indicates the case where there is an error on thesurface of the photoreceptor or on the surface of the image after 10sheets of continuous image formation.

Thus obtained results are presented in TABLE 1 below.

Toner Fluidity Test

20 g of thus obtained toner was sieved with a mesh of a sieve opening of75 μm and the weight of the remaining toner sieved out on the mesh wasmeasured.

Thus obtained results are presented in TABLE 1 below.

Monotone Image Test

As a single color image, a half-tone image made of uniform dots wasformed with “Fantasia 22i” manufactured by TOSHIBA Corporation. Thestate of the roughness of the image was observed by eye.

The evaluation was made on the basis of the following criteria. That is,{circumflex over (∘)} indicates the case where there is no roughnessobserved in the image regardless of the concentration of the half-tone,◯ indicates the case where there is some roughness observed in the imagewhen the half-tone is at a low concentration, Δ indicates the case wherethere is prominent roughness observed in the image when the half-tone isat a low concentration, and X indicates the case where there is aroughness observed when the half-tone is at both low and highconcentrations.

Overall Image Test

Of yellow toner, magenta toner, cyan toner and black toner, toners towhich metal soaps were not added except for the toner of the Example 1described above were used respectively, and general images includingeight kinds of patterns such as persons, for example, black, whiteand/or yellow people, blue sky, green lawn, water flow and flower petalof lily were formed using Fantasia 22i. The state of the roughness ofthe image was visually observed.

The evaluation was made on the basis of the following criteria. That is,{circumflex over (∘)} indicates the case where there is no roughness inany of the eight kinds of patterns, ◯ indicates the case where there isa roughness in some of the patterns, which would not make any problem, Δindicates the case where there is a roughness in all of the eight kindsof patterns, which would not make any problem, and X indicates the casewhere there is a prominent roughness in all of the eight kinds ofpatterns.

Thus obtained results are presented in TABLE 1 below.

Comparative Test 1

As a comparative test, a toner was prepared in the same manner as inExample 1 except that a metal soap was added. With use of this toner,the same tests as in the case of Example 1 were carried out.

Thus obtained results are presented in TABLE 1 below.

Test 2

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 1.0% by weight. With use of thistoner, the same tests as in the case of Example 1 were carried out. Thusobtained results are presented in TABLE 1 below.

Test 3

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 5.0% by weight. With use of thistoner, the same tests as in the case of Example 1 were carried out. Thusobtained results are presented in TABLE 1 below.

Comparative Test 2

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 7.0% by weight. With use of thistoner, the same tests as in the case of Example 1 were carried out. Thusobtained results are presented in TABLE 1 below.

Test 4

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 1.0% by weight and the coloring agentwas changed to 4 parts by weight of Pigment Yellow 180. With use of thistoner, the same tests as in the case of Example 1 were carried out. Thusobtained results are presented in TABLE 1 below.

Test 5

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 1.0% by weight and the coloring agentwas changed to 3 parts by weight of Pigment Blue 15-3. With use of thistoner, the same tests as in the case of Example 1 were carried out. Thusobtained results are presented in TABLE 1 below.

Test 6

A toner was prepared in the same manner as in Example 1 except that theamount of the metal soap added was 1.0% by weight and the coloring agentwas changed to 4 parts by weight of carbon black manufactured byMitsubishi Kagaku K.K. With use of this toner, the same tests as in thecase of Example 1 were carried out. Thus obtained results are presentedin TABLE 1 below.

TABLE 1 Developing Amount of Wear- Single agent's metal soap out Tonercolor Overall Cleaning color added proof fluiding image image errorComparative magenta none 10 μm  1 g ⊚ ⊚ ◯ Text 1 Test 1 magenta Zn-St =0.1% 5 μm 3 g ◯ ◯ ◯ Test 2 magenta Zn-St = 1.0% 2 μm 8 g Δ Δ ◯ Test 3magenta Zn-St = 5.0% 1 μm 11 g  Δ Δ ◯ Comparative magenta Zn-St = 7.0%0.8 μm   12 g  Δ Δ X Test 2 Test 4 yellow Zn-St = 1.0% 2 μm 8 g ⊚ ⊚ ◯Test 5 cyan Zn-St = 1.0% 2 μm 8 g Δ Δ ◯ Test 6 black Zn-St = 1.0% 2 μm 8g Δ ⊚ ◯

From the Comparative Test 1, Tests 1 and 2, it can be understood thatthe amount of the abrasion of the surface of the photoreceptor can beimproved (lessened) by adding a metal soap (zinc stearate). However, atthe same time, as the amount of the metal soap added is increased, thefluidity of the toner is deteriorated. As a result, it is observed thatthe single color image and overall image are deteriorated as well interms of roughness.

From Test 3 and Comparative Test 2, it can be understood that when theamount of the metal soap added exceeds 5%, a cleaning error occurs. Thisis because when the amount of supply of the metal soap is increased, thefriction between the photoreceptor and the cleaning blade issignificantly decreased, and therefore the cleaning cannot besufficiently performed.

In Test 4, excellent images can be obtained in both single color andoverall image evaluations despite the fact that the metal soap wasadded. This is because with regard to the yellow image, the roughnesscannot be well caught in terms of human visual sense. On the other hand,in Test 5, some roughness was observed despite that a similar metal soapwas added. This is because the roughness of a cyan color image can becaught visually more easily as compared to the case of a yellow colorimage.

In Test 6, an excellent image in terms of the overall image evaluationcan be obtained although the image exhibits some roughness in terms ofthe single color image evaluation. This is because a black-color imageis not substantially used in the sections where many observers payparticular attention, such as the color of human skin, a blue sky andthe appearance of the state of a fruit. Further, in such an image, anatural gray color can be reproduced in a gray color region in a betterquality with a so-called process black made of a yellow-color toner, amagenta toner and a cyan toner.

From Comparative Test 2, it can be understood that when the amount ofthe metal soap added per one color exceeds 5%, a cleaning error occurs.Therefore, it is desirable that the amount of the metal soap containedin the four-color developing agents can be preferably 0.01 to 20% byweight. For example, in the case where only the yellow developing agentcontains the metal soap, it is possible that it is added in a range of0.01 to 20% by weight. Further, the yellow developing agent is used, inmost of the cases, as one of four colors in multiple by rotating thephotoreceptor four times, and therefore it would make no problem even if20% by weight of the metal soap is added to the yellow coloring agent.

In the case where the metal soap is added to the black developing agentonly, it is possible to add it in a range of 0.01 to 5% by weight inconsideration of the case where the operation is carried outcontinuously in a monochrome mode.

As Comparative Example 7, a yellow toner having Zn-St=20.0%, magenta,cyan and black toners which do not contain the metal soap, were suppliedto a full-color copier “Fantasia 70” manufactured by TOSHIBA TECH tofill it, and images were formed. Thus obtained images outputted had anexcellent quality in terms of roughness in the single color and overallimage evaluations. In the meantime, in the print wear-out proof test, acleaning error does not occur, or the amount of the abrasion of thelayer on the photo-receptor after 30,000 sheets of a full-color imageformation was as good as 1 μm.

From the tests carried out above, it can be understood that a roughnessof an image can be easily realized visually in the cases of the magentatoner and cyan toner when the metal soap is added to these toners;however a roughness of an image cannot be easily realized visually inthe cases of the yellow toner and black toner even if the metal soap isadded to these toners.

Next, examples in which the metal soap was added to at least the yellowtoner and black toner, and image formation was carried out, will now bepresented.

EXAMPLE 1

A yellow toner similar to that used in Test 4, a black toner similar tothat used in Test 6, a magenta toner similar to that used in ComparativeTest 1, which does not contain the metal soap, and a cyan toner similarto that used in Comparative Test 1, which does not contain the metalsoap, except that Pigment Blue 15-3 in place of Pigment Red 184, wereused in combination and supplied to a full-color copier “Fantasia 70”manufactured by TOSHIBA TECH. Then, the copying operation was carriedout continuously 30,000 times, and the print wear-out proof test wascarried out. The result indicates that the amount of change in thediameter of the photoreceptor after 30,000 times of the copyingoperation was 1.81 μm.

Further, a result of a mark {circumflex over (∘)} was obtained in theoverall image test.

EXAMPLE 2

A yellow toner similar to that used in Test 4, a black toner similar tothat used in Test 6, a magenta toner similar to that used in Test 1, anda cyan toner similar to that used in Test 1 except that Pigment Blue15-3 in place of Pigment Red 184, were used in combination and suppliedto a full-color copier “Fantasia 70” manufactured by TOSHIBA TECH. Then,the copying operation was carried out continuously 30,000 times, and theprint wear-out proof test was carried out. The result indicates that theamount of change in the diameter of the photoreceptor after 30,000 timesof the copying operation was 1.75 μm.

Further, a result of a mark ◯ was obtained in the overall image test.

As described above examples, in the electrophoto-graphic deviceincluding one photoreceptor and a plurality of developing units, thelife of the photoreceptor can be prolonged while maintaining the imagequality and the toner properties, etc., to some degree simply by addingthe metal soap to at least yellow and/or black toners.

Further, in the device, a so-called monochrome mode which forms an imagewith the black toner is used in some cases, and thus in this regard aswell, it is possible to supply a metal soap to the photoreceptor at alltimes if the black toner contains the metal soap. With regard to theroughness of an image formed by the monochrome mode, the requirement forthe image quality is not as severe as the case of the full-color imageas in the case of the conventional monochrome image forming device, andtherefore such a roughness would not make a particular problem.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. An image forming apparatus comprising: an imagecarrier; a plurality of developing devices located to face said imagecarrier and configured to form a developing agent image by developing astatic latent image formed on the image carrier; a transfer deviceconfigured to transfer said developing agent image onto a transfermaterial; a cleaning device provided in a stage behind said transferdevice and configured to collect a remaining developing agent on theimage carrier; and a fixing device having a heating member andconfigured to fix said developing agent image transferred on thetransfer material, wherein said plurality of developing devicescomprise: a yellow-color developing device that contains a yellow-colordeveloping agent containing a yellow coloring agent, a binder resin and0.01 to 5% by weight of a metal soap; a magenta-color developing devicethat contains a magenta-color developing agent containing a magentacoloring agent, a binder resin and a metal soap which is smaller inamount than the metal soap contained in the yellow-color developingagent or which is zero in amount; a cyan-color developing device thatcontains a cyan-color developing agent containing a cyan coloring agent,a binder resin and a metal soap which is smaller in amount than themetal soap contained in the yellow-color developing agent or which iszero in amount; and a black-color developing device that contains ablack-color developing agent containing a black coloring agent, a binderresin and 0.01 to 5% by weight of a metal soap.
 2. An image formingapparatus according to claim 1, wherein said plurality of developingdevices further comprises a magenta-color developing device housing amagenta-color developing agent containing a magenta coloring agent, abinder resin and a metal soap at an amount less than that of said metalsoap contained in said yellow developing agent, and a cyan-colordeveloping device housing a cyan-color developing agent containing acyan coloring agent, a binder resin and a metal soap at an amount lessthan that of said metal soap contained in said yellow developing agent.3. An image forming apparatus according to claim 1, wherein a totalamount of the contents of said metal soap used is 0.02 to 20% by weightof the total weight of the developing agents.
 4. An image formingapparatus according to claim 1, wherein the metal soap is selected fromthe group consisting of zinc stearate, aluminum stearate, calciumstearate, magnesium stearate, zinc behenate, aluminum behenate, calciumbehenate, magnesium behenate, zinc laurate, aluminum laurate, calciumlaurate and magnesium laurate.
 5. An image forming apparatus accordingto claim 1, wherein said plurality of developing device include adeveloping unit having two or more developing devices and a single colordeveloping device provided independent from the developing unit.
 6. Animage forming apparatus according to claim 1, wherein the cleaningdevice includes a cleaning blade.
 7. An image forming apparatusaccording to claim 1, wherein only the yellow-color developing agent andthe black-color developing agent contain the metal soap.
 8. An imageforming apparatus according to claim 1, wherein: the magenta-colordeveloping agent contains a metal soap in an amount of 0.1 to 1.0% byweight, which is smaller in amount than the metal soap contained in theyellow-color developing agent; and the cyan-color developing agentcontains a metal soap in an amount of 0.1 to 1.0% by weight, which issmaller in amount than the metal soap contained in the yellow-colordeveloping agent.
 9. An image forming apparatus according to claim 1,wherein: the magenta-color developing agent contains a metal soap in anamount at which roughness of the image quality does not becomeprominent, and which is smaller in amount than the metal soap containedin the yellow-color developing agent; and the cyan-color developingagent contains a metal soap in an amount at which roughness of the imagequality does not become prominent, and which is smaller in amount thanthe metal soap contained in the yellow-color developing agent.
 10. Animage forming apparatus according to claim 9, wherein: the magenta-colordeveloping agent contains a metal soap in an amount of 1.0% by weight orless; and the cyan-color developing agent contains a metal soap in anamount of 1.0% by weight or less.
 11. An image forming methodcomprising: forming a static latent image on an image carrier; forming adeveloping agent image by using a developing agent optionally suppliedfrom a plurality of developing devices comprising: a yellow-colordeveloping device that contains a yellow-color developing agentcontaining a yellow coloring agent, a binder resin and 0.01 to 5% byweight of a metal soap; a black-color developing device that contains ablack-color developing agent containing a black coloring agent, a binderresin and 0.01 to 5% by weight of a metal soap; a magenta-colordeveloping device that contains a magenta-color developing agentcontaining a magenta coloring agent, a binder resin and a metal soapwhich is smaller in amount than the metal soap contained in theyellow-color developing agent or which is zero in amount; and acyan-color developing device that contains a cyan-color developing agentcontaining a cyan coloring agent, a binder resin and a metal soap whichis smaller in amount than the metal soap contained in the yellow-colordeveloping agent or which is zero in amount; transferring the developingagent image onto a transfer material; cleaning a developing agentremaining on the image carrier after transferring with use of a cleaningunit; and fixing the transferred developing agent image onto a transfermember.
 12. An image forming method according to claim 11, wherein saidplurality of developing devices further includes a magenta-colordeveloping device housing a magenta-color developing agent containing amagenta coloring agent, a binder resin and a metal soap at an amountless than that of the metal soap contained in said yellow developingagent, and a cyan-color developing device housing a cyan-colordeveloping agent containing a cyan coloring agent, a binder resin and ametal soap at an amount less than that of the metal soap contained insaid yellow developing agent.
 13. An image forming method according toclaim 11, wherein a total amount of the contents of the metal soap usedis 0.02 to 20% by weight of the total of the weights of the developingagents.
 14. An image forming method according to claim 11, wherein themetal soap is selected from the group consisting of zinc stearate,aluminum stearate, calcium stearate, magnesium stearate, zinc behenate,aluminum behenate, calcium behenate, magnesium behenate, zinc laurate,aluminum laurate, calcium laurate and magnesium laurate.
 15. An imageforming method according to claim 11, wherein said plurality ofdeveloping device include a developing unit having two or moredeveloping devices and a single color developing device providedindependent from the developing unit.
 16. An image forming methodaccording to claim 11, wherein the cleaning unit includes a cleaningblade.
 17. An image forming method according to claim 11, wherein onlythe yellow-color developing agent and the black-color developing agentcontain the metal soap.
 18. An image forming method according to claim11, wherein: the magenta-color developing agent contains a metal soap inan amount of 0.1 to 1.0% by weight, which is smaller in amount than themetal soap contained in the yellow-color developing agent; and thecyan-color developing agent contains a metal soap in an amount of 0.1 to1.0% by weight, which is smaller in amount than the metal soap containedin the yellow-color developing agent.
 19. An image forming methodaccording to claim 11, wherein the step of forming a developing agentimage comprises supplying a yellow-color developing agent prior tosupplying a magenta and cyan color developing agents.
 20. A combinationof developing agents to be applied to an image forming method apparatusincluding a yellow-color developing device, a magenta-color developingdevice, a cyan-color developing device and a black-color developingdevice which are configured to form a developing agent image bydeveloping a static latent image, comprising: a yellow-color developingagent to be contained in the yellow-color developing device, theyellow-color developing agent containing a yellow coloring agent, abinder resin and 0.01 to 5% by weight of a metal soap; a magenta-colordeveloping agent to be contained in the magenta-color developing device,the magenta-color developing agent containing a magenta coloring agent,a binder resin and a metal soap which is smaller in amount than themetal soap contained in the yellow-color developing agent or which iszero in amount; a cyan-color developing agent to be contained in thecyan-color developing device, the cyan-color developing agent containinga cyan coloring agent, a binder resin and a metal soap which is smallerin amount than the metal soap contained in the yellow-color developingagent or which is zero in amount; and a black-color developing agent tobe contained in the black-color developing device, the black-colordeveloping agent containing a black coloring agent, a binder resin and0.01 to 5% by weight of a metal soap.
 21. A combination of developingagents according to claim 20, further comprising: a magenta-colordeveloping device to be contained in a still another one of saidplurality of developing devices, containing a magenta-color developingagent containing a magenta coloring agent, a binder resin and a metalsoap at an amount less than that of the metal soap contained in theyellow developing agent, and a cyan-color developing agent to becontained in a still another one of said plurality of developingdevices, containing a cyan coloring agent, a binder resin and a metalsoap at an amount less than that of the metal soap contained in theyellow developing agent.
 22. A combination of developing agentsaccording to claim 20, wherein a total amount of the contents of themetal soap used is 0.02 to 20% by weight of the total weight of thedeveloping agents.
 23. A combination of developing agents according toclaim 20, wherein the metal soap is selected from the group consistingof zinc stearate, aluminum stearate, calcium stearate, magnesiumstearate, zinc behenate, aluminum behenate, calcium behenate, magnesiumbehenate, zinc laurate, aluminum laurate, calcium laurate and magnesiumlaurate.
 24. A combination of developing agents according to claim 20,wherein said plurality of developer device include a developing unithaving two or more developing devices and a single color developingdevice provided independent from the developing unit.
 25. A combinationof developing agents according to claim 20, wherein only theyellow-color developing agent and the black-color developing agentcontain the metal soap.
 26. A combination of developing agents accordingto claim 20, wherein: the magenta-color developing agent contains ametal soap in an amount of 0.1 to 1.0% by weight, which is smaller inamount than the metal soap contained in the yellow-color developingagent; and the cyan-color developing agent contains a metal soap in anamount of 0.1 to 1.0% by weight, which is smaller in amount than themetal soap contained in the yellow-color developing agent.